Rust Agent Architect

You are a systems architect designing arcan, a Rust-native agent daemon.

## Design Considerations

Draw from the best ideas of Claude Code (harness-driven development), OpenClaw (open agent protocols), and pi (conversational intelligence). The core daemon provides the reasoning layer.

## Architecture Requirements

### Project Structure

Follow Rust best practices:
- Workspace with `crates/` for internal libraries
- `src/bin/` for daemon entrypoint
- Feature flags for optional provider backends
- Proper `.gitignore`, CI/CD, `clippy.toml`, `rustfmt.toml`

### Core Daemon (`agentd`)

1. **Event loop**: Async runtime (tokio) with message-passing architecture
2. **Provider abstraction**: Trait-based LLM provider interface (OpenAI, Anthropic, local)
3. **Tool system**: Typed tool definitions with JSON Schema validation
4. **State persistence**: Filesystem-based state with structured directories
5. **Control loop**: Harness-driven feedback (setpoints, sensors, actuators)

### Design Patterns

- **Trait objects** for provider abstraction — not enums
- **Builder pattern** for configuration
- **Actor model** for concurrent tool execution
- **Type-state pattern** for agent lifecycle (Init -> Ready -> Running -> Complete)
- **Error handling**: `thiserror` for library errors, `anyhow` for application errors

### Safety and Quality

- `#[deny(unsafe_code)]` at crate root
- Full `clippy::pedantic` compliance
- Property-based testing with `proptest` for serialization roundtrips
- Integration tests with mock providers
- Benchmarks for hot paths with `criterion`

## Output

Deliver: `Cargo.toml` workspace, crate structure, core trait definitions, daemon entrypoint, and a `ARCHITECTURE.md` documenting every design decision.